Honestly, yea its a game and its fictional, but what makes insurgency so wonderful is that it brings the player as close to reality as is possible through a screen. The vast majority of the fanbase care about very minute accuracies of weapons and such, why wouldn't minute details of the general "middle eastern" conflicts this game is very obviously portraying be taken into account as well.
Just by playing the game you can obviously tell that veterans or people who were at least very involved in some way in our contemporary wars made it. It's not just a hardcore shooter, its an experience of modern infantry combat. It's supposed to scare the shit out of you. Especially after this last update, playing the game always comes with a heavy feeling. Even though its a game, the situations we play out are indeed very real. BF1 tried to apply some sort of reverence to soldiers at the start of the game, but insurgency doesn't even need a brutality of war blah blah statement at the opening of the game at all. Just playing makes you, as a character, feel very weak and vulnerable in the face of today's tools of death and destruction. Those of us not involved in the military or today's armed conflicts only see news clips or Hollywood movies which usually glorify or otherwise distort reality. Insurgency SS does such a good job of at least making the player aware of just how scary it all actually is, and it does it by being realistic.
I've gotten called out before for using the word "realistic" instead of "immersive", but I really do mean realistic. Everything the devs have done so far has been to bring the game as close to reality as they can (or so it seems at least). By ignoring reality and letting options for the sake of options interfere with attention to detail, Insurgency will fail to live up to what it has become.
Female players can always play as female characters on the security side. As many people have already gone over, this is realistic and quite common in today's mid-east conflicts. However, for the insurgents, there is a fundamental, dogmatic mandate for women to be subservient. In their eyes, a woman is too weak to fight. The game should reflect this reality.
Finally, I'd like to wrap up my argument with some words on "PC" and sexism. The lack of inclusion of female characters on the insurgent side is not sexist at all in my view. Rather, I find it to be a feminist statement in a way. By failing to include women on the insurgent side, reflecting the reality of the world, the game brings to light a social catastrophe which still exists... gender inequality. Instead of masking the oppression of women to audiences who don't know any better by implementing fictitious equality, perhaps the game will make people ask "why aren't there women insurgent options". Why not? Because there are still large swaths of the world and numerous people who view women as lesser.It makes people realize and stops them from forgetting an important issue. Including female characters on the insurgent side would make the whole issue of gender equality a nonissue and that should be much more dangerous to those concerned about equality than simply having equal options for the sake of everything being nice and tidy and the same.